Tailoring Dense Polyester Nanofiltration Membranes for Selective Mineral Retention in Health-Oriented Potable Water Production

Retaining essential minerals (e.g., Ca²⁺, Mg²⁺) is critical for generating healthy, palatable water. However, conventional polyamide nanofiltration (NF) membranes suffer from excessive mineral salt rejection, chlorine susceptibility, and scaling. Although polyester NF membranes are inherently chlorine-resistant, they lack the precise selectivity required for safe, mineral-rich potable water, limiting their application in drinking water treatment. Herein, we developed a high-selectivity dense polyester NF membrane using 3,5-dihydroxybenzoic acid (DHBA) as an aqueous monomer and incorporated sodium dodecyl sulfate (SDS) to assist interfacial polymerization by enhancing trans-interface reactant diffusion, creating membranes with a uniform pore size distribution. By tuning the SDS concentration, the optimal polyester membrane (SAIP-DHBA-0.125) achieved a water permeance of 8.3 L m^-2 h^-1 bar^-1, superior water/Na₂SO₄ and CaCl₂/Na₂SO₄ selectivities (42.7 and 177.7, respectively), and enhanced antiscaling and chlorine resistance, surpassing reported polyester membranes, most lab-made polyamide NF membranes, and a commercial nanofiltration membrane (NF270, Dupont). When applied to real tap water with high hardness, the SAIP-DHBA-0.125 membrane produced a high-quality permeate that complies with the Standards for Healthy Drinking Water Quality (T/BJWA 001-2021), while retaining essential minerals (Ca²⁺: 37.6 mg L^-1, Mg²⁺: 56.3 mg L^-1), approximately 55% higher than the NF270 membrane. Moreover, it maintained ∼96.0% of its initial flux and stable total dissolved solids rejection during 96 h of operation, underscoring its potential for the sustainable production of health-oriented potable water.